Picking specific units from a selection

[andy5995]

@Trensicourt mentioned this

When you have many different types of units selected and they should up in the upper right corner, players should be able to click on the specify type of unit to select.

Example, If 5 archers and 3 axe indians are selected, clicking the icon for the axe indian should select only the axe indian.

This is partly dependent on #146